Dendrochronology and dendroclimatology of yew in Poland.

This study concerns dendrochronology and dendroclimatology of yew growing in Poland. The yew (Taxus baccata L.), a long-lived, slow-growing tree, is regarded as a species threatened with extinction. The eastern boundary of its range transects Poland. The analyses were performed on 34 yew populations which are protected as parts of nature reserves, as nature monuments, or which are planned to be protected. Samples were collected using Pressler borer from a total of 774 trees yielding 1307 profiles. Classical dating techniques (including cross-dating method) were subsequently used to reconstruct 34 local chronologies. Average tree-ring width was 0.84 mm and ranged from 0.27 to 1.47 mm. For most stands, the age of the yew trees is overestimated. The studied populations most frequently are 100–200 years old, and the oldest yew trees in Poland are growing in the KS population (age estimated at 500–600 years). Average tree-ring width was found to be strongly dependent on the chronology length/tree age. The 674 pointer years calculated for the local chronologies served as a basis for determining pointer years for the entire study area. Negative years include: 1862, 1865, 1917, 1927, 1940, 1947, 1956, 1963, 1969, 1976, 1979, 1993, 1996, and 2003. Positive years are: 1884, 1914, 1916, 1965, 1977, 1988, 1997, and 2007. Analysis of weather conditions in those years demonstrated a strong relationship between tree-ring width and air temperature in winter, pre-spring, and early spring. Higher-than-average temperatures during those seasons correlate positively with yew tree-ring width. Response function analysis performed for local and regional chronologies point to a dominant role of air temperature in December of the year preceding growth and in January, February, and March of the current year (linear relationships). June precipitation is an additional factor affecting tree-ring width in some areas of northern and northwestern Poland: the higher the precipitation, the wider the tree-rings. The results obtained, particularly those concerning growth-climate relationships and dendroclimatic regionalisation, can be used in the on-going programme of yew restitution in Poland. • Yew trees growing in Poland, on most stands, are less than 200 years old, but their age is often overestimated. The oldest yew population in Poland is 500–600 years old. • The yew is a slow-growing species – average tree-ring width is only 0.84 mm. • Tree-ring width in yew trees depends on winter and early spring air temperature (cold winters and late onset of spring cause a decrease in tree-ring width). [ABSTRACT FROM AUTHOR]